Process for producing spherical activated carbon

ABSTRACT

Disclosure is made of a specific process for producing activated carbon in spherical form, starting with organic polymer spherules based on styrene and divinylbenzene, wherein said polymer spherules contain chemical groups leading to the formation of free radicals and thus to cross-linkages by their thermal decomposition, in particular sulfonic acid groups. Furthermore, various application purposes for the thus-produced activated carbon spherules are named.

[0001] The present invention relates to a process for producingactivated carbon, particularly in spherical form (“carbon spherules”),as well as activated carbon products produced in this way and their usefor various applications, in particular for filters or protectivematerials, such as protective suits.

[0002] Due to its rather unspecific adsorptive properties, activatedcarbon is the most widely used adsorbent. Legal regulations as well asan increased sense of responsibility for the environment has led to anincreasing demand for activated carbon.

[0003] Activated carbon in general is obtained by smoldering(carbonization, pyrolysis) and subsequent activation of carbonaceouscompounds, wherein those compounds are preferred which lead toeconomically reasonable yields, because the losses in weight, caused bythe separation of volatiles in the carbonization step and by burning offin the activation step, are considerable. For further details onactivated carbon production, reference can be made, e.g., to H.v. Kienleand E. Bäder, “Aktivkohle und ihre industrielle Anwendung” (ActivatedCarbon and the Industrial Use thereof), published by Enke Verlag,Stuttgart, 1980.

[0004] However, also the nature of the produced activatedcarbon—microporous or macroporous, solid or brittle—depends on thestarting material. Common starting materials are coconut shells, chipsof wood, turf, pit coal, pitches, as well as special plastics, which,inter alia, play a certain role in the production of activated carbonfabrics.

[0005] Activated carbon is used in various forms: pulverized coal,splint coal, granular coal, molded coal (cylinders of activated coal)and, since the end of the 70's, also spherical activated carbon (“carbonspherules”). Spherical activated carbon, being distinct from other formsof activated carbon, such as pulverized coal, splint coal, granular coaland the like, has a number of advantages, making it valuable—or evenindispensable—for certain applications: it is flowable, enormouslyresistant to abrasion (dust-free), and very hard. Because of the highprices, however, the use thereof is essentially restricted to protectivesuits and high-quality filters for pollutants in air streams.

[0006] Carbon spherules, due to their specific form, as well as due totheir extremely high resistance to abrasion, for example, in particularareas of application, such as surface filters for protective suitsagainst chemical poisons and filters for low pollutant concentrations inlarge quantities of air, are in high demand. Thus, when loadingreticulated, macroporous polyurethane foams with activated carbonaccording to DE 38 13 563 A1, only a readily flowable coal can beemployed if also the internal layers of the foam material are to beoptimally coated. In the production of protective suits against chemicalpoisons in accordance with DE 33 04 349 C3, for example, also onlyhighly abrasion-resistant coal may be employed, and solely carbonspherules fulfill that requirement.

[0007] Today, carbon spherules are, for the most part, still produced inmulti-stage and very sophisticated processes. The best-known process isthe production of spherules from coal-tar pitch and suitable asphalticresidues from petroleum chemistry, which—in order to becomeunmeltable—are oxidized, carbonized and activated. For example, carbonspherules can also be produced in a multistage process, starting frombitumen. These multi-stage processes are very expensive and thecorrespondingly high price of these carbon spherules precludes their usefor many applications in which carbon spherules should actually bepreferred due to their properties.

[0008] Consequently, attempts were made to produce high-grade carbonspherules in a different way.

[0009] From the state of the art it is known to produce spherical carbonby carbonization and subsequent activation of fresh or spention-exchangers containing sulfonic acid groups, or by carbonization ofion-exchange precursors in the presence of sulphuric acid and subsequentactivation wherein sulfonic acid groups or sulphuric acid have thefunction of a crosslinker, the yields—regardless whether starting fromfinished cation exchangers or unsulfonated ion-exchange precursors—beingapprox. 30 to 50%, based on organic or polymeric starting material. Forexample, such processes are disclosed in DE 43 28 219 A1 and DE 43 04026 A1, as well as DE 196 00 237 A1, including the German supplementaryapplication DE 196 25 069. However, these methods are unfavorable andproblematic, particularly because large amounts of sulfur dioxide arereleased—approx. 1 kg of SO₂ per 1 kg final product—and because of,inter alia, the associated corrosion problems with the productionequipment. When using spent ion-exchange resins, in particular spentcation-exchange resins, as starting materials, an additional problemarises in that the same—in spite of being washed with acid—arecontaminated with cations, which then accumulate in the final productsuch that the production of larger quantities of carbon spherules havingidentical quality is consequently very difficult. When usingion-exchange precursors, i.e. polymer spherules without exchanger groups(sulfonic acid groups), in addition large amounts of sulphuric acidand/or oleum for cross-linking during carbonization are required.

[0010] WO 98/07655 discloses a process for producing activated carbonspherules, wherein firstly a mixture comprising a distillation residuestemming from diisocyanate production, a carbonaceous processing aid,and, optionally, one or several additional additives is processed intoflowable spherules and then the thus-obtained spherules are subjected tocarbonization and a subsequent activation step. In this process, too,large amounts of decomposition products are released discontinuously,which is associated with the above-mentioned problems.

[0011] Therefore, it is an object of the present invention to provide anovel process for producing activated carbon, particularly in the formof spherules, which is expected to avoid—at least in part—thedisadvantages described above and which are related to the processes ofthe prior art. At the same time, such a process should enable a lesssophisticated, possibly less cost-intensive production of activatedcarbon. In particular, in the case that the starting materialscontaining sulfonic acid group are used, the process should facilitatethe disposal of the SO₂ that is generated.

[0012] It is a further object of the present invention to provide aprocess for producing activated carbon, particularly in spherulous form,which allows for the possibility of also employing—in addition toalready-known starting materials for activated carbon production—newstarting materials which have heretofore not yet been used for theproduction of activated carbon.

[0013] Applicant has now surprisingly discovered that the problem dealtwith by the present invention may be solved by separating from eachother the procedural steps required in the production of activatedcarbon—namely carbonization on the one hand and activation on the otherhand—and by carrying out carbonization in a continuous manner whilecarrying out re-carbonization and activation in a discontinuous manner.In particular, the present invention is based on the separation of thecorrosive phase (pre-carbonization step, in connection with SO₂ output)from the high-temperature phase (activation). Applicant has surprisinglydiscovered that the pre-carbonized starting material is no longercorrosive, i.e. by further increasing the temperature, corrosive agentsis no longer be generated.

[0014] Thus, a subject-matter of the present invention is a process forproducing spherical activated carbon by carbonization and activation ofpolymer spherules based on styrene and divinylbenzene, wherein saidspherules contain functional chemical groups, especially sulfonic acidgroups, said chemical groups leading to the formation of free radicalsand thus to cross-linkages by their thermal decomposition, wherein saidpolymer spherules are first subjected to a continuous pre-carbonizationstep and then are discontinuously treated in a re-carbonization andactivation step.

[0015] In the smoldering step—synonymously also referred to as“carbonization” or “pyrolysis” and with reference to the presentinvention consisting of pre-carbonization and re-carbonization—thecarbonaceous starting material is converted into carbon, or in otherwords, the starting material is carbonized. During smoldering of theabove-mentioned, in particular porous and/or gel-like organic polymerspherules based on styrene and divinylbenzene and containing functionalchemical groups (particularly sulfonic acid groups), said functionalchemical groups which lead to the formation of free radicals and thus tocross-linkages by their thermal decomposition, are destroyed—whileseparating volatiles, such as especially SO₂; thus, free radicals areformed that cause strong cross-linkages—in the absence of which therewould not exist a pyrolysis residue (i.e. carbon) after all. In general,pyrolysis is conducted in an inert atmosphere (e.g. nitrogen), or—atmost—under slightly oxidizing atmosphere. Similarly, it may beadvantageous during smoldering, in particular at higher temperatures(e.g. ranging from approx. 500° C. to 650° C.) to add a minor amount ofoxygen, especially in the form of air (e.g. 1 to 5%) to the inertatmosphere to cause oxidation of the carbonized polymer backbone and tothus facilitate the activation.

[0016] According to the present invention, continuous pre-carbonizationmay be carried out, for example, in a rotary tube, working continuouslyand having a temperature gradient of from 100° C. to 850° C., preferablyfrom 100° C. to 650° C. Total duration should be approx. 1 hour toapprox. 4 hours, preferably approx. 2 hours to approx. 3 hours. In sodoing, particularly, the carbonized material should reach a temperatureof from 400° C. to 800° C., preferably 550° C. to 600° C. As mentionedabove, preferably inert conditions (e.g. nitrogen), or at best slightlyoxidizing conditions should be applied.

[0017] Subsequently, the continuously carbonized material may becollected in a preferably heat-insulated vessel and, when the fillingcapacity of said heat-insulated vessel is reached, may then beintroduced into a rotary tube, working discontinuously for furtherpyrolysis (re-carbonization) and subsequent activation.

[0018] During carbonization, particularly re-carbonization, a smallamount of oxygen or air, respectively, (e.g. approx. 1 to 5%) may beadded to the inert gas (e. g. nitrogen), especially in the range ofhigher temperatures (e.g. in the range from approx. 500° C. to approx.650° C.). This may facilitate activation, as it is discussed in furtherdetail in the following.

[0019] Carbonization, according to the invention, comprisingpre-carbonization and re-carbonization, is followed by activation. Thelatter is performed under conditions known per se. The basic principleof activation is to decompose a portion of the carbon generated in thecarbonization step in a selective and targeted manner under appropriateconditions. In so doing, numerous pores, fissures and cracks aregenerated and the surface area, in respect to the unit of mass,increasey considerably. Thus, in the activation step, coal is burned offin a selective manner. Because carbon is decomposed during activation,in part a considerable loss in substance occurs in this process, which,under optimal circumstances, is tantamount to an increase in porosityand an increase of the internal surface (pore volume). Activation,therefore, takes place under selective or controlled oxidizingconditions, respectively. Usual activation gases generally includeoxygen, in particular in the form of air, water vapor and/or carbondioxide, as well as mixtures of these activation gases. As oxygen posesthe risk that the impact is not only selective, but occurs on the totalsurface—thus burning off the carbon to a higher or lesser degree—watervapor and carbon dioxide are given preference. Water vapor isparticularly preferable, optionally in admixture with an inert gas (e.g.nitrogen). To obtain a technically sufficient high reaction rate,activation is performed in general at temperatures ranging from approx.800° C. to approx. 1000° C.

[0020] According to the present invention, activation may especially becarried out with a mixture of water vapor and nitrogen, in particular attemperatures of from approx. 850° C. to approx. 960° C., preferably fromapprox. 910° C. to approx. 930° C. The durations may range from approx.2 hours to approx. 5 hours, preferably approx. 2 hours to approx. 3hours.

[0021] The process of the present invention, for example, may beperformed in such a manner that at first the continuouspre-carbonization is carried out within the first 80 minutes to 120minutes at temperatures of up to approx. 650° C., preferably at approx.500° C., in which step the largest part of the SO₂ is expelled and then,after completing re-carbonization, activation at approx. 850° C. toapprox. 950° C., in particular at approx. 910° C. to approx. 930° C. iseffected, wherein the activation takes—depending on the desired innersurface of the activated carbon spherules and the volume or fillinglevel of the rotary tube—approx. 2 hours to approx. 5 hours and, as anactivation gas, preferably water vapor in nitrogen, especiallypreferable approx. 25% water vapor in nitrogen, is employed.

[0022] According to the present invention, as a starting material forthe inventive production of spherical activated carbon, polymer organicspherules based on styrene and divinylbenzene are employed, containingfunctional chemical groups, said chemical groups leading to theformation of free radicals and thus to cross-linkages as a result oftheir thermal decomposition, in particular acidic groups, such assulfonic acid groups. As starting materials, for example, organicpolymer spherules can be used, having a polymer backbone substantiallyconsisting of polystyrene, wherein the polystyrene chains may be, atsome spots, connected or cross-linked, respectively, through a componenthaving at least two vinyl groups per molecule, in particulardivinylbenzene, and the polymer skeleton may contain functional chemicalgroups, particularly sulfonic acid groups, said chemical groups leadingto the formation of free radicals and thus to cross-linkages as a resultof their thermal decomposition. In particular, the starting materialused, according to the present invention, for the production ofspherical activated carbon is organic polymer spherules based onpolystyrene and having divinylbenzene cross-linkages wherein saidpolymer spherules comprise functional chemical groups, particularlyacidic groups, like sulfonic acid groups, said chemical groups leadingto the formation of free radicals and thus to cross-linkages by theirthermal decomposition; therein, the divinylbenzene content, based onpolymer spherules, may be up to approx. 20%, particularly up to approx.15%, preferably up to approx. 10% by weight. Instead of divinylbenzene,for the cross-linking of polystyrene, however, a comparable organic, inparticular aromatic organic compound suitable for the cross-linking ofpolystyrene and having at least two cross-linking groups per molecule(in particular vinyl groups) may also be employed.

[0023] The polymeric starting material, for example, may be present in aporous, particularly macroporous, and/or gel-like form. In case ofgel-like starting materials, microporous polymer particles arepreferably used. Macroporous or microporous, gel-like starting materialsare preferably used.

[0024] Since the form or shape of the polymeric starting material issubstantially maintained in the carbonization and pyrolysis steps—thecarbonization and activation however leading to a reduction in particlesize or particle diameter—the production of activated carbon inspherical form also has to start with polymer spherules, i.e. polymersin spherical form or approximately spherical form. In general, polymerspherules used in accordance with the present invention have diametersof up to approx. 2 mm, in particular of up to approx. 1.5 mm or less.

[0025] According to the first embodiment of the present invention, thechemical functional groups, leading to cross-linkages upon carbonizationor pyrolysis, particularly sulfonic acid groups, are already present inthe starting material. It is preferable in this embodiment that theweight ratio of polymer/functional groups or polymer/sulfonic acidgroups, respectively, is approx. 2:1 to approx. 1:1.

[0026] Examples of polymeric starting materials, in which the functionalchemical groups leading to cross-linkages during the carbonization orpyrolysis steps, particularly sulfonic acid groups, are already presentin the actual starting material, are ion-exchange resins, in particularstrongly acidic cation-exchange resins, i.e. cation exchange resinshaving sulfonic acid groups. These can either be unspent or also spention-exchange resins. In the case of spent cation exchangers, they can becontaminated with metal ions, which are then present in the finalproduct as a catalytic metal impregnation.

[0027] In the case that it is started with spent or unspention-exchangers, the present invention relates also to a process fordisposing spent or unspent ion-exchangers. Hence, the process of thepresent invention is capable of converting spent ion-exchangers, to bedisposed of, into a useful product—i.e. activated carbon—which, due toits property to adsorb environmental poisons, contributes to theprotection of the environment.

[0028] Further examples of polymeric starting materials, in which thefunctional chemical groups, leading to cross-linkages during thecarbonization or pyrolysis steps, particularly sulfonic acid groups, arealready present in the actual starting material, are acidic organiccatalysts, for example catalysts for the synthesis of bisphenols or thesynthesis of MTBE (MTBE=methyl-tert. butyl ether), preferably sulfonicacid group containing organic catalysts. Particularly preferred areacidic organic catalysts of the type as described above, which areporous and/or gel-like.

[0029] For, applicant has surprisingly discovered that, for example,acidic organic catalysts accumulating in the synthesis of MTBE orbisphenols and which have become inactive, are a good starting materialfor the production of carbon spherules. The spherical catalyst materialoriginating from the reactor for the synthesis of bisphenol or MTBE maythen, optionally after a washing and drying step, be carbonized andactivated in a manner in accordance with the present invention. Phenol,which still adheres in the case of catalysts, resulting from thesynthesis of bisphenol, is destroyed in the carbonization or pyrolysisstep and/or burnt off in the post-combustion step. The yields ofactivated carbon spherules in the case of organic catalysts are similarto those of cation exchangers. Contrary to spent ion-exchangers,however, with spent organic catalysts no accumulation of cations in thecarbon is to be expected. According to the present invention, as thestarting materials, spent or exhausted acidic organic catalystsresulting from the synthesis of MTBE or from the synthesis of bisphenolsfrom phenol and acetone, which accrue as a waste material, are readilyemployable and thus can be conveniently disposed of.

[0030] In the case of starting from acidic organic polymeric catalystsbased on styrene and divinylbenzene, which are spent or have becomeinactive, in particular from the synthesis of MTBE or bisphenols, thepresent invention also relates to a process for the disposal ofcatalysts which are spent or have become inert. The inventive process isable to convert waste, to be disposed of, into a useful product—i.e.activated carbon—which, by virtue of its property to adsorbenvironmental poisons, contributes to the protection of the environment.

[0031] Also in this first embodiment of the present invention, accordingto which the functional chemical groups leading to cross-linkages duringthe carbonization or pyrolysis steps, particularly sulfonic acid groups,are already present in the original starting material, an amount of from5 to 25% SO₃ in the form of sulphuric acid and/or oleum may be addedbefore and/or during the carbonization step, especially to increase theyield of carbon spherules. Thereby, the periods of pre-carbonization maybe shortened, for example to approx. 30 to approx. 120 minutes, inparticular approx. 30 to approx. 90 minutes or less.

[0032] It was found that the yields of carbon spherules are improved, asthe acid content of the starting material, in particular ion-exchangersor catalysts, increases. Thus, as mentioned above, particularly in thecase of ion-exchangers or catalysts having a low acid content, someoleum and/or sulphuric acid may be added in order to improve the yield.Normally, for example, approx. 5 to approx. 25% of bound or free SO₃,based on the polymer portion in the starting material, are sufficient.

[0033] According to a second embodiment of the present invention, thefunctional chemical groups, leading to cross-linkages during thecarbonization or pyrolysis steps, particularly sulfonic acid groups, arenot yet present in the original starting material but still have to begenerated in situ. Preferably, this is done by introducing said chemicalfunctional groups leading to cross-linkages, in particular sulfonic acidgroups, only with the beginning, i.e. before and/or during saidpre-carbonization step. This may, for example, be accomplished by theaddition of SO₃, in particular in the form of oleum, optionally inadmixture with sulphuric acid, before and/or during pre-carbonization tosaid polymeric organic starting material in spherical form. Here, theweight ratio polymer/oleum 20% may be particularly approx. 1:1 or theweight ratio polymer/oleum 20%/sulphuric acid may be in particularapprox. 1:1:0.5, respectively.

[0034] Examples of such starting materials, according to this secondembodiment, in which the functional chemical groups leading tocross-linkages, particularly sulfonic acid groups, are not yet presentin the actual starting material, but have to be generated in situ beforeand/or during pre-carbonization, are precursors of ion-exchangers, i.e.organic polymer spherules without functional groups which must besulfonated before and/or during carbonization, for example by additionof SO₃ in the form of oleum or sulphuric acid.

[0035] The precursors of ion-exchangers may basically be gel-like ormacroporous. The latter are much more expensive, primarily because oftheir considerably higher divinylbenzene content. The numerous mesoporesthereof remain completely intact during the conversion to activatedcarbon, which is useful for some applications. The gel-types, however,lead to markedly microporous coals: the pore volume can be present up to90 to 95% as micropores. The gel types often contain approx. 2 toapprox. 8% divinylbenzene. However, also types with only weakcross-linkages, having lower contents of divinylbenzene (approx. 2 to 4%divinylbenzene) survive the heavy swelling in the acid, i.e. they do notburst or break up into hemispheres. It has become evident that alsotypes with a very low divinylbenzene content are well suited accordingto the present invention. Sulfonation, which has to be as complete aspossible, is much more important because in the decomposition ofsulfonic acid groups, those free radicals are produced that lead to thecross-linking being responsible for the yield.

[0036] When employing precursors of ion-exchangers (i.e. pure polymers),gel types are preferred, whereas when starting from cation exchangers,both macroporous and gel types can be employed, the selection beingrather based on economic considerations. The reason is that macroporousprecursors absorb very large amounts of acid or oleum into their largepores—similar to a blotter—such that the mixture of polymer and acid isdry or sandy, and the uniform distribution of acid can hardly beachieved. Apart from that, however, carbonization and activation ofcation exchangers lead to comparable products, as if starting fromprecursors plus acid.

[0037] The particle size of the obtained carbon spherules depends on thesize of the spheres in the starting material. Commercial base productsin general lead to activated carbon spherules with a diameter of fromapprox. 0.2 mm to approx. 1.0 mm, in particular approx. 0.3 to approx.0.8 mm.

[0038] For example, the process according to the invention can betypically carried out as follows:

[0039] Suitable polymeric, spherical starting material, containingsulfonic acid groups, based upon styrene and divinylbenzene, e.g. cationexchangers or organic acidic catalysts, are introduced into a rotarytube, working continuously and having a temperature gradient of fromapprox. 100° C. to approx. 850° C., and preferably approx. 100° C. toapprox. 650° C., and are pre-carbonized. The duration may then be fromapprox. 1 to 2 hours, for example. A final temperature of at leastapprox. 550° C. should be reached.

[0040] When working, for example, with precursors of ion-exchangers,i.e. polymer spherules based on styrene and divinylbenzene, having nofunctional groups, e.g. sulphuric acid and/or oleum may be blown in atthe front end of the rotary tube, e.g. at approx. 100° C., the rotarymovement ensures thorough mixing, which should preferably be finishedbefore temperatures of approx. 200° C. are reached, which is not aproblem with the appropriate internal fittings. For example, 1 partpolymer spherules (ion-exchange precursors) plus 1 part oleum 20% plus ½part sulphuric acid 98% produced very good results, whereby the excessin liquid phase herein provides particularly good mixing.

[0041] The hot, pre-carbonized material can then be collected in avessel, which preferably should be heat-insulated until a charge for thediscontinuously working rotary tube is collected.

[0042] Subsequently, the preferably still hot, pre-carbonized, flowablematerial may be subjected to final pyrolysis (re-carbonization) in adiscontinuously working rotary tube, and be activated in a manner thatis well known to those skilled in the art. Since the activation takes acomparatively long time, a continuously working rotary tube for thisprocessing step is not viable because it would have to be extremelylong. Depending on the degree of activation, yields of carbon spherulesof from 50 to 75%, with respect to polymeric starting material, wereachieved.

[0043] As mentioned above, activation may be facilitated by adding,during re-carbonization, particularly in a range from approx. 500° C. toapprox. 650° C., a small amount of oxygen, particularly in the form ofair (e.g. approx. 1 to 5%) to the inert gas. This leads to the oxidationof the carbonized polymer skeleton, which, by splitting off oxygen as COat from approx. 700° C. to approx. 750° C., leads to an initialporosity, which promotes activation in the interior of the bulk. Theactivation may be performed, for example, with air, CO₂ and/or H₂O(water vapor), preferably with water vapor, optionally in mixture ordilution with an inert gas (e.g. nitrogen). Good results, for example,were obtained with a ratio water vapor/inert gas of approx. 1:3.

[0044] Thus, as an example, the process of the present invention can becarried out such that the starting material is continuouslypre-carbonized at temperatures of up to a maximum of approx. 850° C.,preferably of up to a maximum of approx. 650° C., then, optionally, thepre-carbonized material is collected in a vessel, and finally it isdiscontinuously re-carbonized and activated at temperatures from approx.850° C. to approx. 950° C., in particular approx. 910° C. to approx.930° C., under per se known conditions, preferably with water vapor(optionally in mixture or dilution with an inert gas, such as nitrogen),wherein in the pre- and/or re-carbonization steps, optionally, a smallamount of oxygen, especially in the form of air (e.g. approx. 1 to 5%)can be added to the inert gas, particularly at temperatures from approx.500° C.

[0045] While in processes known from the state of the art, wherein bothcarbonization and activation steps are performed batch-wise ordiscontinuously, very large amounts of corrosive SO₂ accrue in batches,causing problems with disposal or handling, in the process according tothe present invention, however, SO₂ is released in a continuous mannerduring the continuous pre-carbonization step, which enormouslyfacilitates the disposal or handling thereof. In fact, except in theprocess starting from pit coal-tar pitch, processes known in the priorart have the common feature that, per kg of final product, very largeamounts of SO₂, namely approx. 1 kg, are released, the release of SO₂primarily taking place between approx. 300° C. and approx. 450° C., thatis, at SO₂ peaks, thus making disposal enormously difficult.SO₂-washers, in the state-of-the-art processes, have to be adapted tothe SO₂ peaks such that they are completely over-dimensioned for therest of the time of the process, and the recovery of SO₂ is verydifficult.

[0046] Therefore, there was an urgent need to substantially facilitatethe disposal of SO₂ occurring in the activated carbon production, inparticular during pyrolysis or carbonization. The solution according tothe present invention is to carry out pre-carbonization, which issubstantially completed at approx. 600° C., on a continuous basis suchthat a uniform output of SO₂ (and of some volatile hydrocarbons) takesplace while the activation is performed in a discontinuous manner.

[0047] The advantages of separating the acidic phase (pre-carbonization)from the high-temperature phase (activation) are numerous:

[0048] 1. The continuously working rotary tube for pre-carbonization canbe made of particularly acid-proof types of steel, which are lesssuitable for high temperatures, whereas the discontinuously workingrotary tube (re-carbonization and activation) can be made of steel thatis especially suitable for high temperatures. In other words, separationof the comparatively fast, corrosive stage, under the release of a greatamount of SO₂ (pre-carbonization), from the comparatively slowactivation enables an optimal adaptation of the equipment being used.Since, for example, pre-carbonization in the presence of acid may onlyrequire approx. 60 to approx. 120 minutes, whereas the activation,however, takes several hours, the rotary tube for pre-carbonization mayhave smaller dimensions than the rotary tube forre-carbonization/-activation (The long duration in the large rotary tubefor the activation is also the reason why it is not operated on acontinuously working basis because the required length thereof would beenormous.).

[0049] 2. Washers (washing devices) for SO₂ may have much smallerdimensions than those of state of the art processes because no SO₂ peakshave to be handled anymore, but SO₂ output is continuous and uniform.

[0050] 3. Regular, continuous output of SO₂ in the process of thepresent invention allows its recovery, in particular in connection witha catalytic oxidation to SO₃, and, optionally, further conversion intosulphuric acid or oleum, respectively, which can be much more favorablydisposed of than sulfite liquor, or may even be re-employed orre-circulated in the process according to the present invention, forexample especially when employing precursors of ion-exchangers asstarting material.

[0051] 4. The process of the invention provides the opportunity todispose of waste products, as it is the case for spent ion-exchangersand spent catalysts, and to convert them into useful products, i.e.activated carbon spherules. According to the process of the presentinvention, highly useful, high-quality, abrasion-resistant activatedcarbon spherules, are obtained at good yields also from waste materialsto be disposed of, which otherwise would have to be disposed of inanother way—in particular they would have to be burnt off or stored.Therein lies another advantage of the present invention, especially intimes of increasing environmental awareness. Thus, anothersubject-matter of the present invention is equally a process fordisposing of as well as regenerating waste materials.

[0052] In addition, another subject-matter of the present invention isproducts obtained or obtainable according to the process of the presentinvention, i.e. activated carbon in spherical form.

[0053] As mentioned before, the particle size of carbon spherulesobtained depends on the starting material. Commercial starting productslead, in general, to activated carbon spherules with diameters of fromapprox. 0.2 mm to approx. 1.0 mm, in particular diameters from approx.0.3 mm to approx. 0.8 mm, with average diameters from approx. 0.4 mm toapprox. 0.5 mm. During carbonization and activation, the spherical formof the starting materials is preserved, i.e., through the form of thestarting materials, the particle size of the final product may beselectively controlled and determined, representing another advantage ofthe process according to the present invention.

[0054] The diameter of the thus produced activated carbon spherules isapprox. 0.1 mm smaller than that of the starting polymer spherules suchthat, through appropriate selection of the starting material, thediameter of carbon spherules may be controlled. For most applications,spherule diameters of from approx. 0.2 mm to approx. 1.0 mm, inparticular approx. 0.3 mm to approx. 0.8 mm, with average diameters ofapprox. 0.4 mm to approx. 0.6 mm, are particularly suitable.

[0055] By activation, internal surfaces of from approx. 800 m²/g toapprox. 1500 m²/g are obtainable, preferably being approx. 900 m²/g toapprox. 1200 m²/g. Bursting pressure for an individual activated carbonspherule in general is approx. 5 Newton to approx. 20 Newton. Apparentdensity is approx. 400 g/l to approx. 800 g/l, preferably approx. 500g/l to approx. 750 g/l.

[0056] Carbon spherules obtained in accordance with the invention, arehighly abrasion-resistant—abrasion is up to 100 times less than that ofgood grain carbon—flowable, dust-free, and highly pressure-resistant.Thus, another subject-matter of the present invention is activatedcarbon spherules having a high strength, in particularabrasion-resistance, which can be produced in accordance with theprocess of the present invention.

[0057] Of major importance to the activity of carbon spherules are thepores of activated carbon, in particular the micropores having adiameter of up to approx. 20 Å, since these lie within the order ofmagnitude of most molecules to be adsorbed. In general, the majorportion of the inner surface of activated carbon is owed to microporesas well. In addition, the so-called mesopores—sometimes referred to astransitional pores or supply pores—with diameters of from approx. 20 toapprox. 500 Å are also of importance. Furthermore, a portion of evenbigger macropores exists. By selection of raw materials and proceduralsteps during the activation, the properties of the final products can beselectively controlled. A higher proportion of micropores is desirable.

[0058] To those skilled in the art, it is known that pore volume, porediameter, and pore distribution vary depending on the degree ofactivation, and the pore system and pore structure, in particular thepore diameter, as well as the surface structure of the final product maybe influenced selectively by the temperature and activation, such thatin this regard, reference can be made to the pertinent technicalliterature.

[0059] Activated carbon spherules produced through the process accordingto the invention, exhibit from good to excellent adsorption properties.

[0060] Moreover, there is a possibility to influence or modify theadsorption properties of activated carbon spherules produced accordingto the invention by impregnation with catalysts (enzymes, metals, suchas e.g. copper, silver, platinum, chromium, zinc, mercury, palladium,cadmium, iron, etc., as well as compounds of these metals). Thus, theactivated carbon product obtained according to production process of theinvention may also comprise a catalytically effective component,preferably a compound of a catalytically active metal. Impregnation ofactivated carbon with catalysts is per se well known to those skilled inthe art, so that reference can be made in this regard to pertinenttechnical literature.

[0061] Activated carbon spherules produced according to the process ofthe present invention, can be used in any number of differentapplications. Activated carbon spherules produced according to theprocess of the present invention, for example, can be used in theproduction of adsorbent materials such as adsorption (surface) filters,filter mats, odor filters, surface filters for protective suits,particularly for civil and/or military purpose, ambient air purifyingfilters, gas mask filters, and adsorbing substrate structures, or, forprotective materials, in particular protective suits against chemicalpoisons such as warfare agents, or else for filters, particularlyfilters for removing of pollutants, toxic agents and/or odorous agents(odorants) originating from air or gas streams.

[0062] Another subject-matter of the present invention, therefore, isalso the adsorption materials containing activated carbon spheruleswhich are produced in accordance with the present invention,particularly filters of any kind such as adsorbent (surface) filters,filter mats, odor filters, surface filters for protective suits,particularly for civil and/or military purpose, such as protective suitsagainst chemical poisons such as warfare agents, ambient air-purifyingfilters as well as protective suits produced therefrom, gas-maskfilters, filters for removing of pollutants, toxic agents and/or odorousagents (odorants) originating from air or gas streams and adsorbingsubstrate structures.

[0063] The present invention is now illustrated by way of workingexamples, which shall in no way be restrictive toward the presentinvention.

[0064] In reading the description and examples, one skilled in the artwill be able to conceive numerous other designs, variations, ormodifications of the present invention, without deviating from the scopeof the present invention.

WORKING EXAMPLES Example 1

[0065] 1000 g of gel-like, spherical, porous polymer, said polymer beingbased on styrene and 4% divinylbenzene, was wetted with 750 g of oleum20%. The acid was absorbed within a few minutes, resulting in a stillsomewhat flowable product. The latter was then fed into a rotary tube,working continuously and having a temperature gradient, andpre-carbonized during 30 minutes (total duration). After the acid hadbeen eliminated substantially in form of SO₂ and H₂O, a total of 940 gof brilliant, black spherules was obtained. After being kept in aheat-insulated vessel for a short period of time they were then fed intoa discontinuously working rotary tube in one charge, while still hot,and re-carbonized therein and activated at 925° C. with watervapor/nitrogen in a ratio of 1:3 over a period of three hours.

[0066] As a result, 645 g of carbon spherules (iodine number: 950) wereobtained with an average diameter of 0.45 mm, a bursting pressure perspherule of ≧1000 g, an apparent density of 660 g/l, and an ash contentof ≦0.1%. The carbon spherules had a pore volume of approx. 0.5 ml/g,consisting of at least 90% micropores.

Example 2

[0067] In a beaker, 1000 g of precursor from DOWEX HCR-S, a precursorfor a cation-exchange resin, were mixed with 750 g of sulphuric acid and250 g of oleum with 20% SO₃. Within a few minutes, sulphuric acid wascompletely absorbed while the polymer spherules were swelling.

[0068] This material was pre-carbonized in a rotary tube, workingcontinuously and exhibiting a temperature gradient. The rotary tubeconsisted of a quartz (silica) tube (Ø 40 mm, length 800 mm), which washeated up to 650° C. and purged with some nitrogen. Steel wire woundinto spiral form in the interior of the tube, provided for the transportof the contents. The rotary tube was continuously filled with a mixtureof precursors and sulphuric acid at the non-heated end thereof and therotational speed was regulated to 50 such that, in the hot zone, aduration of 20 minutes was achieved. The other end of the tube wasloosely sealed with a tin container having a circular aperture, in whichpre-carbonized material was collected. As a result, a total of 820 g ofblack, dry, and flowable spherules were obtained. Thereby, a total ofapprox. 500 g of SO₂ and some carbonaceous, non-identifiable productshad been split. A tarry condensate was not observed.

[0069] The pre-carbonized material was then subjected to furtherprocessing in a discontinuously working rotary tube, supplied by PLEQCo., i.e. subjected to re-carbonization and activation. Within 45minutes, 500° C. had been reached. At this temperature, 5% of air wereadded to the purge gas (nitrogen) and heated up to 650° C. in thefollowing 45 minutes. Then, 25% of water vapor was added to the purgegas, and the temperature was brought to 900° C. within 30 minutes. Thefinal temperature was maintained for 90 minutes. After cooling downunder nitrogen to 400° C., the rotary tube was emptied. As a result, 490g of excellent carbon spherules with an interior surface (BET) of 1200m²/g and an average diameter of 0.46 mm were obtained.

Example 3

[0070] Example 2 was repeated, except that to 1000 g of precursormaterial 1000 g of oleum 20% and 500 g of sulphuric acid were added. Ahighly flowable mixture was obtained. Duration in the continuouslyworking rotary tube was increased to 90 minutes. 1090 g of black, dry,and flowable spherules were obtained, which were activated to a BETsurface of 950 m²/g. The yield was 790 g.

1. Process for producing spherical activated carbon (activated carbonspherules) by carbonization (pyrolysis, smoldering) and activation ofpolymer spherules based on styrene and divinylbenzene, wherein saidpolymer spherules comprise chemical groups, particularly sulfonic acidgroups, said chemical groups leading to the formation of free radicalsand thus to cross-linkages by their thermal decomposition, characterizedin that said polymer spherules are first subjected to a continuouspre-carbonization step and are then discontinuously treated inre-carbonization and activation step.
 2. Process according to claim 1,characterized in that said chemical groups, particularly sulfonic acidgroups, leading to cross-linkages are already present in the startingmaterial and/or that the weight ratio polymer/sulfonic acid groups isabout 2:1 to about 1:1.
 3. Process according to claim 1 and/or 2,characterized in that said starting material is selected from the groupconsisting of ion-exchangers, particularly strongly acid ion-exchangers,and/or acid organic catalysts, such as catalysts for the synthesis ofbisphenols or the synthesis of methyl-tert.-butyl ether (MTBE). 4.Process according to claim 3, characterized in that an amount of about 5to about 25% SO₃, preferably in the form of sulphuric acid and/or oleum,is added to said ion-exchangers, preferably strongly acidion-exchangers, and/or to said acid organic catalysts before and/orduring said carbonization step.
 5. Process according to claim 1,characterized in that said sulfonic acid groups are introduced beforeand/or during said carbonization step, particularly by addition of SO₃,preferably in the form of oleum, optionally in mixture with sulphuricacid.
 6. Process according to claim 5, characterized in that the weightratio polymer/oleum 20% is about 1:1.
 7. Process according to claim 5,characterized in that the weight ratio polymer/oleum 20%/sulphuric acidis about 1:1: 0.5.
 8. Process according to one or more of the precedingclaims, characterized in that said polymer spherules are porous,particularly macroporous, and/or gel-like.
 9. Process according to oneor more of the preceding claims, characterized in that saidcarbonization step is carried out in a reaction vessel, particularlyrotary-tube, working continuously and having a temperature-gradient offrom about 100° C. to about 850° C., preferably from about 100° C. toabout 650° C., and preferably with a total residence time of about 1 toabout 4 hours, preferably about 2 to about 3 hours, more preferablyabout 60 to about 90 minutes, particularly wherein the carbonizedmaterial may reach a temperature of about 400° C. to about 800° C.,preferably about 550° C. to about 600° C.
 10. Process according to oneor more of the preceding claims, characterized in that said the materialpre-carbonized is continuously collected in a heat-insulated vessel and,when the filling capacity of said heat-insulated vessel is reached, isthen introduced into a reaction vessel, particularly rotary tube,working discontinuously for further pyrolysis (re-carbonization) andsubsequent activation.
 11. Process according to one or more of thepreceding claims, characterized in that said activation is carried outwith a mixture of steam (water-vapor) and nitrogen and particularly attemperatures of from about 850° C. to about 960° C., preferably fromabout 910° C. to about 930° C., particularly with a residence time ofabout 2 to about 5 hours, preferably about 2 to about 3 hours. 12.Process according to one or more of the preceding claims, characterizedin that SO₂ continuously expulsed particularly during pre-carbonizationis regenerated, in particular by catalytic oxidation to SO₃ and furtherprocessing to sulphuric acid and/or oleum.
 13. Activated carbonspherules obtainable by the process according to claims 1 to 12,particularly with an inner (internal) surface of from about 800 m²/kg toabout 1.500 m²/kg, preferably from about 900 m²/kg to about 1.200 m²/kg,and/or with a diameter of from about 0.2 mm to about 1.0 mm, preferablyfrom about 0.3 mm to about 0.8 mm, with an average diameter of fromabout 0.4 mm to about 0.6 mm and/or with a bursting pressure of fromabout 5 Newton to about 20 Newton per spherule and/or with an apparentdensity of from about 400 to about 800 g/l, preferably from about 500 toabout 750 g/l.
 14. Use of spherical activated carbon obtainable by theprocess according to one or several of claims 1 to 12, for producing ofadsorbent materials such as adsorption (surface) filters, filter mats,odor filters, surface filters for protective suits, particularly forcivil and/or military purpose, ambient air purifying filters andadsorbing substrate structures.
 15. Use of spherical activated carbonobtainable by the process according to one or several of claims 1 to 12,for a protective material, particularly for protective suits againstchemical poisons such as warfare agents, or for filters, particularlyfor removing of pollutants, toxic agents and/or odorous agents(odorants) originating from air or gas streams.
 16. Adsorbent materials,particularly filters of all kinds such as adsorbent (surface) filters,odor filters, surface filters for protective suits, particularly forcivil and/or military purpose, such as protective suits against chemicalpoisons such as warfare agents, ambient air purifying filters as well asprotective suits produced therefrom, gas mask filters, filters forremoving of pollutants, toxic agents and/or odorous agents (odorants)originating from air or gas streams, filter mats and adsorbing substratestructures, comprising spherical activated carbon obtainable by theprocess according to any of claims 1 to 12.